Impact reinforced composite panel

ABSTRACT

A composite panel having front and back faces, the panel comprising facing reinforcement, backing reinforcement and matrix material binding to the facing and backing reinforcements, the facing and backing reinforcements each independently comprising (i) one or more reinforcing sheets and/or (ii) one or more generally planar arrays of longitudinally arranged, spaced apart, reinforcing rods which are interconnected by means for resisting increase of the spacing distance between adjacent rods, at least one rod array (ii) being present in the facing and/or backing reinforcement wherein the means for resisting increase of the spacing distance between adjacent rods is transverse filamentary interlacing of rods in the array, the facing reinforcement being located on or embedded in matrix material adjacent to the front face of the panel, the backing reinforcement being located in a plane or planes substantially parallel to the plane or planes of the facing reinforcement, and being substantially coextensive therewith, and spaced therefrom by matrix material.

This invention relates to reinforced composite panels, useful as barrier elements for shielding structures, equipment and personnel from blast and/or ballistic impact damage.

There is a need for blast and/or ballistic (i.e. projectile) impact resistant barrier structures for use in battle zones or in locations near explosive hazard sites, to shield and protect buildings, accommodation units, equipment, personnel and other vulnerable entities. It would be convenient if such barrier structures could be assembled from one or more prefabricated or on-site constructed panels, supported and interconnected in an appropriate fashion using panel support elements and/or interconnection elements for interconnecting adjacent panels or for connecting panels to structural elements of a building, container or other entity which it is intended to shield. It is an object of this invention to provide a panel for such use.

According to the invention, there is provided a composite panel having front and back faces, the panel comprising facing reinforcement, backing reinforcement and matrix material binding to the facing and backing reinforcements, the facing and backing reinforcements each independently comprising (i) one or more reinforcing sheets and/or (ii) one or more generally planar arrays of longitudinally arranged, spaced apart, reinforcing rods which are interconnected by means for resisting increase of the spacing distance between adjacent rods, at least one rod array (ii) being present in the facing and/or backing reinforcement wherein the means for resisting increase of the spacing distance between adjacent rods is transverse filamentary interlacing of rods in the array, the facing reinforcement being located on or embedded in matrix material adjacent to the front face of the panel, the backing reinforcement being located in a plane or planes substantially parallel to the plane or planes of the facing reinforcement, and being substantially coextensive therewith, and spaced therefrom by matrix material.

The term “generally planar” when used in relation to an array of rods present in facing or backing reinforcement means that the rods lie side by side on a notional flat or curved surface. Inherent in the fact that reinforcing sheets present in facing or backing reinforcement are in sheet format is the requirement that they too conform to a flat or curved surface. Hence, the requirement that the backing reinforcement is located in a plane or planes substantially parallel to the plane or planes of the facing reinforcement is to be interpreted as meaning that the surfaces associated with the facing and backing reinforcements are matching and complementary, and that the gap between the two surfaces is generally uniform. The requirement that the backing reinforcement be substantially coextensive with the facing reinforcement may be expressed equivalently by the requirement that the reinforcements have generally the same overall area, and the overall shapes defined by their perimeters are generally the same.

The overall shape of the panel will be determined by end use requirements. Often panels of the invention will be generally flat, with generally uniform thickness. For more specialised end use requirements, a panel may be shaped with a radius or radii of curvature, or may be formed in two or more intersecting planes. Whatever its overall shape, the fact that it is a panel implies that its thickness will be smaller than its other dimensions, e.g. its length and width, and it will have two faces separated by its thickness. For the purposes of constructing the panel, the front face is that which will face the direction from which blast or ballistic impact is expected, and the other is the back face.

Likewise, the overall dimensions of the panels of the invention will be determined by end-use requirements, such as the impact conditions which they are required to resist, and the size and/or area of the object which the panel or an assembly of the panels is required to protect. In many cases, the dimensions of a rectangular panel of the invention may be, for example, in the following ranges: thickness 10 to 500 mm, length 0.5 to 50 meters, width 0.5 to 30 meters.

Facing reinforcement may be located on the front face of the panel, or wholly or partially embedded in matrix material adjacent the front face of the panel. For present purposes, reinforcement is deemed adjacent the front face of the panel if it is located closer to the front face than to the back face of the panel. In one embodiment, facing reinforcement is located on the matrix material of the front face of the panel and adheres thereto. In another embodiment, facing reinforcement is at least partially embedded in the matrix material of the front face of the panel. In yet another embodiment, the facing reinforcement has at least two layers, at least one of which is wholly embedded in matrix material, and another is bound to the front face of the panel by matrix material or is itself wholly or partially embedded in matrix material. Facing reinforcement may advantageously be located on or embedded in matrix material formulated to be harder than matrix material present elsewhere in the panel.

For present purposes, reinforcement is considered backing reinforcement if it is closer to the back face of the panel than to the front face of the panel, or if it is located on the median plane or surface between the two panel faces. In one embodiment, backing reinforcement is located on, and is bound by matrix material to, the back face of the panel. In another embodiment, backing reinforcement is at least partially embedded in the matrix material of the back face of the panel. In yet another embodiment, the backing reinforcement has at least two layers, at least one of which is wholly embedded in matrix material, and another is bound to the back face of the panel by matrix material or is itself wholly or partially embedded in matrix material. Backing reinforcement may advantageously be located on or embedded in matrix material formulated to be more ductile than matrix material present elsewhere in the panel.

Subject to the requirement that at least one interlaced rod array must be present, facing and backing reinforcements may comprise perforated or unperforated sheet material (for example of metal such as steel, or fibre reinforced resin such as glass or carbon fibre reinforced resin) or rod arrays (for example of metal such as steel, or of fibre reinforced resin such as glass or carbon fibre reinforced plastics).

The panels of the invention are sandwich structures wherein a matrix material is sandwiched between the facing and backing reinforcements. As is discussed below, where the facing and/or backing reinforcements themselves comprise layers of sheet and/or rod array reinforcements (again provided at least one interlaced rod array is present), matrix material may also be sandwiched between such layers, although the thicknesses of such inter-layer matrix material will generally be small compared to the thickness of the matrix layers between the facing and backing reinforcements. The volume fraction of facing and backing reinforcement in panels of the invention may typically lie in the range from 20 to 60%. Often the facing and/or backing reinforcements may comprise steel sheet materials or steel rods, and in such cases typically steel with a yield strength in the range 1000 to 2500 MPa may be used.

The facing reinforcement may have one or a plurality, for example two or three layers of reinforcement, each layer being independently an array of rods, or a perforated or unperforated sheet material. At least the layer of facing reinforcement nearest the front face of the panel may be of hard materials such as ceramic or hardened steel e.g. that available under the trade names Hardox 600 or Armox 600, or of softer materials such as a high strength steel with a hard coating such as a chromium surface of thickness about 20 to 500 μm. Individual layers of the facing reinforcement may be separated by a matrix-filled gap, such filled gap providing so-called “soft impact” effects. Alternatively, individual layers of the facing reinforcement may abut each other, providing so-called “hard impact” effects. At least the layer of facing reinforcement nearest the front face of the panel may be embedded or partially embedded in a hard particle-reinforced matrix which is harder than elsewhere in the panel. In addition, the rods or sheet materials of the facing reinforcement may be pre-stressed.

The backing reinforcement also may have one or a plurality, for example, two or three layers of reinforcement, each layer being independently a rod array, or a perforated or unperforated sheet material. Individual layers of the backing reinforcement may also be separated by a matrix-filled gap. The rods or sheet materials of the backing reinforcement may also be pre-stressed. The backing reinforcement, or any of the reinforcement layers comprising the backing reinforcement, may be of lightweight materials such as fibre reinforced resin materials.

Rod arrays are formed by longitudinally arranged, spaced apart, reinforcing rods which are interconnected by means for resisting increase of the spacing distance between adjacent rods. The spacing between rods will normally be narrower than the diameter of any projectile which the panel is intended to resist. To penetrate the array, such a projectile would have to rupture the rods of the array or force its way between adjacent rods. The latter eventuality is minimised according to the invention by the interconnection of the rods by means to resist increase in the spacing distance between rods. One preferred means of doing so is by transverse filament (e.g. wire, or a monofilament thread, or a multifilament thread, string or rope, such as metal wire, aramid fibre, carbon fibre, or glass fibre) interlacing of rods in the array, whereby the rods are tied to a fixed spacing by the transversely extending interlacing filament(s). Panels of the invention must have at least one such interlaced rod array as or as part of the facing or backing reinforcement. Two arrays of rods may also be superimposed at an angle, for example a right angle, to each other, at least one array being interlaced as discussed above, and ties, welds or glue bonds formed at the nodes of the resultant grid serve to resist increase of the spacing between rods of each grid, and separation of the individual arrays of the grid. In one such embodiment, two arrays of rods are superimposed at an angle, for example a right angle, to each other, the rods of each array are transversely interlaced to tie the rods to a fixed spacing, and the interlacing filaments are arranged to be twisted around each or selected intersections of the superimposed arrays to tie the arrays together at such intersections. The transverse filamentary interlacing serves not only to resist increase in spacing between rods in individual arrays, but also to resist out of plane relative movement of the individual arrays. In such an embodiment, the interlacing filaments of one of the rod arrays are preferably positioned substantially colinearly with the rods of the other array, so that filamentary interlacings do not extend across the open cells of the grid defined by the superimposed rod arrays.

As to the spacing of the rods in an array or the diameter or configuration of the perforations in sheet reinforcement, it is desirable that these parameters be selected taking into account the thickness, the tensile strength, and the deformation capacity of the reinforcement, so that the reinforcement maintains a high contact pressure between it and the projectile during its penetration.

Facing or backing reinforcement may include at least two types of material; for example, one type of rod or sheet material may be lighter than the other. Thus, the heavier material may be metallic such as steel or high strength, high ductility metal matrix composite, and the lighter material may be resinous, such as carbon or glass fibre reinforced resin.

Whatever their structures, it is preferred that the facing and backing reinforcements are interconnected and/or anchored in the matrix material to resist out-of-plane relative movement. This may be done using interconnecting bolts, welded or glued interconnecting short rods or studs, or by wire or cable ties between the facing and backing reinforcements. Where the facing and/or backing reinforcements are made up of two or more layers of sheets and/or rods, as described above, it is preferred that each layer of the respective facing or backing reinforcements are also interconnected and/or anchored in the matrix.

To reduce splintering or fragmentation under impact, it is usually preferred that there should be no substantial layer of matrix material exposed on the front or back face of the panel.

In the panels of the invention, the facing and backing reinforcements are spaced from each other by matrix material. In some cases that spacing may be sufficiently wide to accommodate panel support elements, such as rods or beams, arranged between the front and back reinforcement. Such support elements may project beyond the perimeter of the panel to provide means for connection of two or more panels in the assembly of a protective structure.

The matrix material of the panel may be cementitious, ceramic, metallic or resinous. Cementitious matrix materials will often be preferred. An example is the DSP (“Densified systems containing uftrafine Particles”) matrix materials disclosed, e.g., in U.S. Pat. Nos. 5,234,754 and 4,588,443 which may be based on dense packing of cement particles with ultrafine particles, for example silica fume particles, in interstices between the cement particles. A preferred matrix, is made from a mix containing cement particles, ultrafine microsilica particles of a size which is typically about 1/100 of the size of the cement particles, water in a low amount relative to the cement plus microsilica, a concrete superplasticizer as dispersing agent, and silica or carborundum sand, often with added steel fibres. Typically, DSP matrices may have compressive strength in the range 200 to 400 MPa, tensile strength in the range 10 to 50 MPa, modulus of elasticity in the range 30 GPa to 100 GPa, and fracture energy in the range 1 KN/m to 100 KN/m.

Preferably the matrix material in the panels of the invention is a DSP material, in which the microfine binder particles are of silica or fly ash, and which includes metal fibres, preferably a high loading of steel fibres such as from 14-17% by dry mix volume. Stone aggregate and sand may also be present in cementitious DSP matrix materials.

Panels of the invention may be fabricated by casting hardenable matrix material on or around the facing and backing reinforcements and their interconnectors and/or anchors (if any). Intimate contact between matrix material and the various reinforcement and other components of the panel may be improved by vibration treatment of the cast structure before hardening. Hardening/curing may be assisted by elevated temperatures.

Means of interconnection between facing and backing reinforcements, or between multiple layers thereof can be introduced prior to casting the matrix material, or after casting. For example, when the means of interconnection is a series of nut and bolt fasteners, the panel can be drilled to accommodate the fasteners after the cast matrix material has hardened or partially hardened. Alternatively bore-formers sized to accommodate the bolts can be arranged between pre-drilled holes in the reinforcement sheets, and the matrix material cast around the bore-formers as the assembly is built up. The bolts can then be inserted in the bore holes after the matrix material has hardened or partially hardened. Still another possibility is to dispense with bore-formers, and simply cast the matrix material around the interconnection means after complete or partial interconnection of the reinforcement sheets.

When constructing panels by laying down the reinforcement layer by layer, and casting the matrix material onto each successive layer as it is laid down, the assembly can be vibrated as it is cast or after casting but before the matrix material is set, to ensure good contact between the matrix material and the reinforcement, and to reduce the risk of air bubbles in the matrix material. In that latter connection, if the topmost reinforcement layer of the assembly is a sheet material, it is often desirable to include in the panel construction blow that sheet a liner layer of a material which is permeable to air, such as a fibrous matting, for example felt. During vibration of the panel assembly air is then vibrated from the matrix material into the permeable layer, from which it can be expressed at the panel edges.

When a panel of the invention suffers blast and/or ballistic impact the arrangement of facing and backing reinforcement bound by matrix material resists and absorbs impact force, assisted by the matrix. The impact force causes substantial tensile stresses at the back of the panel. Under such tension, matrix material exposed on the back face will tend to splinter and fragment, a process also known as spalling, and there may be a risk of flying fragments behaving like shrapnel and causing damage to the structures, equipment, personnel or other entities shielded by the panel. Preferably, therefore, the back face of the panel is adapted to resist spalling when the front face of the panel is subjected to impact force. Such adaptation might take the form of a more ductile (i.e. more spalling-resistant) layer of matrix material on the back face of the panel than in the panel interior. The ductility of the surface layer might be achieved by incorporating a large amount of long fibres. Alternatively, spalling resistance might be provided by a flexible fragment-containment layer covering the back face of the panel. For example of a layer of fibre reinforced epoxy resin may be formed on the back face of the panel. Alternatively, a flexible sheet of, for example, synthetic rubber might be fixed or laminated to the back face of the panel. If the backing reinforcement comprises sheet(s) located on the back face, and if these sheets are interconnected with the facing reinforcement or anchored in the matrix to resist out-of-plane relative movement as described above, those sheets also serve to resist spalling.

Similarly, when the front face of the panel suffers blast or ballistic impact force, any matrix material exposed on the face may also tend to splinter and throw off fragments which might damage equipment or personnel within range. Such splintering and fragmentation of the front face (often called scabbing) can be minimised by increased ductility of the matrix material adjacent the front face, and/or by fixing a fragment-containment layer to cover the front face of the panel, as discussed above in the case of the back face.

The invention will now be further illustrated by reference to the accompanying drawings, wherein

FIGS. 1A to 1C show (diagrammatically) possible arrangements of facing and backing reinforcement in longitudinal cross sections of panels of the invention; and

FIG. 2A to 2C depict details of rod array reinforcement for use in panels of the invention.

In FIG. 1A, a rectangular panel 1 of the invention is shown truncated lengthwise, with a front face facing to the left as indicated by the arrow A, with facing reinforcement 2 and backing reinforcement 3 located in or on matrix material 4. Backing reinforcement 3 is substantially equidistant from the facing reinforcement 2. Backing reinforcement 3 is substantially coextensive with facing reinforcement 2 in that the two define the length and width of the panel. Backing reinforcement 3 is spaced from facing reinforcement 2 by matrix material 4 in that matrix material fills the gap between the two. In a preferred embodiment, the matrix material 4 is a cement-based DSP material reinforced with steel fibres as described above.

At least one of the facing and backing reinforcements must be a transversely interlaced rod array as discussed herein. Subject to that requirement there are many combinations of reinforcement types which could be used:

Facing reinforcement 2 could be, for example one of the following

-   -   Type f1: 2 layers of rod arrays laid at right angles to each         other     -   Type f2: 2 layers of perforated sheets     -   Type f3: 3 layers of rod arrays, the middle array being laid at         right angles to the others.     -   Type f4: 3 layers of perforated sheets     -   Type f5: 1 top layer of perforated sheet and 1 layer of rod         array     -   Type f6: 1 layer of unperforated sheet     -   Type f7: 1 top layer of unperforated sheet and 2 bottom layers         of rod arrays laid at right angles to each other     -   Type f8: 1 layer of perforated sheet     -   Type f9: 2 layers of unperforated sheets         Where facing reinforcement 2 consists of two or three layers         (Types f1, f2, f3, f4 f5, f7, and f9 above) it is embedded in         the matrix material of the front face of the panel, with the         leftmost layer adhered to or partially embedded in matrix         material so that the matrix cover at the panel face is reduced         to a minimum. The individual reinforcing layers are spaced by a         thin (e.g. 2 mm) layer of matrix to soften impact on the panel.         Where the facing reinforcement consists of a single layer,         (Types f6 and f8 above) it is adhered to or partially or         minimally embedded in matrix material so that the matrix cover         at the panel face is reduced to a minimum. The matrix in which         the facing reinforcement is embedded or to which it is adhered         may be made to harder specification than the matrix between the         facing reinforcement 2 and the back face of the panel. Also, a         hard coating may be applied to the facing reinforcement or to         the leftmost layer which experiences the first impact. Where         reinforcement is adhered to the surface of a face of the panel,         keying elements such as studs may be provided on the contact         side of the reinforcement, these keying elements then becoming         embedded in the matrix material and improving binding to the         reinforcement. Where potential scabbing of the front face of the         panel is a concern, the matrix in which the facing reinforcement         is embedded or to which it is adhered may be made to a more         ductile specification than the matrix between the facing         reinforcement 2 and the back face of the panel; and/or a         separate scab liner (i.e. a flexible fragment-containment layer,         for example a resinous or rubbery layer) located on the front         face of the panel may be desirable.

Backing reinforcement 3 could be, for example one of the following

-   -   Type b1: 1 layer of rod array     -   Type b2: 1 layer of closely spaced rod array     -   Type b3: 1 layer of perforated sheet     -   Type b4: 2 layers of rod array laid at right angles to each         other     -   Type b5: 1 layer of rod array and 1 layer of closely spaced rod         array nearest the back face of the panel, laid at right angles         to each other     -   Type b6: 2 layers of perforated sheets     -   Type b7: 1 layer of unperforated sheet     -   Type b8: 2 layers of rod arrays laid at right angles to each         other and 1 layer of unperforated sheet (at back face of panel).

Again, where backing reinforcement 3 consists of two or three layers (Types b4, b5, b6 and b8 above) it is embedded in the matrix material of the back face of the panel, with the rightmost layer adhered to or only partially or minimally embedded in matrix material so that the matrix cover at the panel face is reduced to a minimum. The individual reinforcing layers are again spaced by a thin (e.g. 2 mm) layer of matrix to soften impact on the panel. Where the backing reinforcement consists of a single layer, (Types b1, b2, b3 and b7 above) it is adhered to or partially or minimally embedded in matrix material so that the matrix cover at the panel face is reduced to a minimum. The matrix in which the backing reinforcement is embedded or to which it is adhered may be made to a more ductile specification than the matrix between front face of the panel and the backing reinforcement. Where reinforcement is adhered to the surface of a face of the panel, keying elements such as studs may be provided on the contact side of the reinforcement, these keying elements then becoming embedded in the matrix material and improving binding to the reinforcement. With backing reinforcement of Types b1, b3, b4 and b6, a separate spall liner (i.e. a flexible fragment-containment layer, for example a resinous or rubbery layer) located on the back face of the panel may be desirable. With embodiments of Types b2, b5, b7 and b8, the sheet or closely spaced rod array at the back face of the panel acts as its own fragment-containment layer, so a separate spall liner may not be needed.

Preferred combinations of types of facing and backing reinforcement are f1+b4 (and here the b4 rod arrays at the back face of the panel may be composed of lighter rods); f2+b3; f3+b1; f6+b7; f7+b8; f8+b3; f9+b7; f7+b7; f7+b4.

In FIG. 1B, the rectangular panel of FIG. 1A is shown with facing reinforcement 2, matrix material 4, and backing reinforcement 3 all as discussed in relation to FIG. 1A. In this case however, facing reinforcement 2 and backing reinforcement 3 are interconnected by elements 7, which may be, for example rods, studs, spacer blocks, or honeycomb spacer fillets which are welded or glued to the reinforcement with which they are in contact, or bolts which may pass through facing and backing reinforcement. Where the facing and/or backing reinforcement consists of two or more layers, those layers are preferably also interconnected. In this way, relative out of plane movement of the facing and backing reinforcement is resisted when the front face of the panel suffers impact. Forces are transferred from the facing reinforcement through the interconnections to the backing reinforcement, and the composite of facing and backing reinforcement tends to deform as a unit. The same principle of interconnecting the facing and backing reinforcement applies irrespective of the structure of the reinforcements (whether plate or rod grids or other constructions) and irrespective of the mode of interconnection (whether bolts, welded or glued rods or studs, spacer blocks, honeycomb spacer fillets, or other structures).

In FIG. 1C, the rearward part of a panel of the invention is shown, again with backing reinforcement 3 as discussed in relation to FIG. 1A and matrix material 4. A flexible fragment containment membrane 6 is adhered to the back face of the panel to contain any splinters of fragments which might fly from the back face when the front face of the panel is impacted. The membrane 6 may be, for example, a rubbery sheet adhered to the matrix material by a bonding agent, or, if backing reinforcement is exposed on the back face of the panel, it may be tied or otherwise anchored to the reinforcement. Alternatively, membrane 6 may be a layer of fibre-reinforced resin. Such a layer may be sprayed directly onto the back face of the panel, or during panel fabrication the matrix material of the panel may be cast against the resin layer, either directly or via an intermediate layer of bonding aid such as a fibrous mat.

In FIG. 2A, a segment of a panel reinforcement in the form of the required transversely interlaced rod array is illustrated. It comprises a layer of generally parallel rods 1, laced together by filamentary material such as wire aramid string or rope, indicated at 2, wrapped or knotted around the rods at tie points, two of which are indicated at T. Only three interlacing filaments 2 are shown, but in practice there may be many such interlacings, spaced along the length of the rods.

The interlacings shown in FIG. 2A serve to resist increase of the spacing distance between adjacent rods of the array, such as may otherwise occur if a projectile or fragment were to attempt to force itself through the array. There are many ways of improving the efficiency of the interlacing for that purpose. For example, the style of knot around the rods may play a part. FIG. 2B shows the formation of a knot around a rod 1 which when tensioned, will often will be suitable. The knot of FIG. 2B loops twice around the rod with a crossover location which enables the filamentary interlacing 2 to stretch linearly along the upper or lower plane of the layer of rods, as shown diagrammatically in cross section in FIG. 2C. In FIG. 2C, the filament 2 loops around rods 1, with crossover points 3 on the top plane of the rod array, producing a lacing pattern as shown in FIG. 2A. Often it will be desirable to have double interlacing, as shown diagrammatically in FIG. 2D, with one set of interlacings 4 running along the lower plane of the rod array 1 with filament crossover points 5, and a second set of interlacings 2 running along the upper plane of the rod layer with filament crossover points 3. Such double interlacing reduces the likelihood of rods rolling in the plane of the array as a projectile or fragment attempts to force a way through.

If desired, these interlacing principles may be used in interlacings between facing and backing reinforcement or between separate backing and facing reinforcements.

In FIG. 2E a segment of a panel reinforcement in the form of a rod array, comprises a layer of generally parallel rods 1, with additional rods, two of which are shown as 2 and 3, laid on the array at right angles thereto. The additional rods 2 and 3 are shown as more widely spaced than the rods 1 of the array, but might be spaced similarly to rods 1, effectively to form a second array overlying the first. At their intersections rods 1 of the lower array and rods 2 and 3 are joined so that the latter then serve as means to resist increase of the spacing distance between adjacent rods 1, and vice versa. Joining of the rods at their intersections might be by means of welds or glue spots. However, in FIG. 2E, the lower rod array has been transversely interlaced by filaments, for example of wire, as in FIG. 2A, but the filaments additionally tie the two rod layers at the intersection points. The ties T are indicated in FIG. 2E at intersections, and one of the interlacing filaments 4, is exposed by the cutaway right hand end of rod 3. It will be appreciated that the filaments run generally colinearly with the rods of the upper array so that they are not exposed to or fragment impact by traversing the open cells of the grid, and are in effect shielded by the upper rod array. The transverse interlacing 4 of the lower array may be single as in FIG. 2C or double as in FIG. 2D. The upper rod array too might be transversely interlaced with the filaments running essentially colinearly with rods of the lower array. Also, the rod arrays might be interlaced separately as discussed in relation to FIGS. 2A-D, and the ties T at the intersections might be separately tied from short individual filaments. 

1. A composite panel having front and back faces, the panel comprising facing reinforcement, backing reinforcement and matrix material binding to the facing and backing reinforcements, the facing and backing reinforcements each independently comprising (i) one or more reinforcing sheets and/or (i) one or more generally planar arrays of longitudinally arranged, spaced apart, reinforcing rods which are interconnected by means for resisting increase of the spacing distance between adjacent rods, at least one rod array (ii) being present in the facing and/or backing reinforcement wherein the means for resisting increase of the spacing distance between adjacent rods is transverse filamentary interlacing of rods in the array, the facing reinforcement being located on or embedded in matrix material adjacent to the front face of the panel, the backing reinforcement being located in a plane or planes substantially parallel to the plane or planes of the facing reinforcement, and being substantially coextensive therewith, and spaced therefrom by matrix material.
 2. A panel as claimed in claim 1 wherein the facing and/or backing reinforcements are each independently constituted by a plurality of layers of reinforcing sheets and/or reinforcing rod arrays.
 3. A panel as claimed in claim 2 wherein some or all of the adjacent layers in the facing or backing reinforcement are spaced from each other by a gap filled with matrix material.
 4. A panel as claimed in claim 1 wherein at least two adjacent rod arrays are present in the facing and/or backing reinforcement, one array being laid at an angle to the other, in at least one of which of which the means for resisting increase of the spacing distance between adjacent rods is transverse filamentary interlacing of rods in the array.
 5. A panel as claimed in claim 4 wherein ties and/or welds and/or glue bonds are formed at the nodes of the resultant grid of rods as additional means for resisting increase of the spacing distance between adjacent rods.
 6. A panel as claimed in claim 4 wherein the two arrays of rods are superimposed at an angle to each other, the rods of each array are transversely interlaced to tie the rods to a fixed spacing, and the interlacing filaments are arranged to be twisted around each or selected intersections of the superimposed arrays to tie the arrays together at such intersections.
 7. A panel as claimed in claim 1 wherein the facing and backing reinforcements, and optionally any plurality of reinforcement layers constituting the facing and/or backing reinforcements, are interconnected and/or anchored in the matrix material, to resist out-of-plane relative movement.
 8. A panel as claimed in claim 1 wherein the facing reinforcement is located on or embedded in matrix material formulated to be harder than matrix material present elsewhere In the panel.
 9. A panel as claimed in claim 1 wherein the backing reinforcement is located on or embedded in matrix material formulated to be more ductile than matrix material present elsewhere in the panel.
 10. A panel as claimed in claim 1 wherein the facing reinforcement or at least one layer thereof is harder than the backing reinforcement or any layer thereof.
 11. A panel as claimed in claim 1 wherein the matrix material is cementitious, metallic, ceramic or resinous.
 12. A panel as claimed in claim 11 wherein the matrix material includes fibres and/or silica or carborundum sand.
 13. A panel as claimed in claim 1 wherein the matrix material is cementitious and includes steel fibers.
 14. A panel as claimed in claim 13 wherein the cementitious matrix material is a DSP material.
 15. A panel as claimed in claim 1 wherein the back and/or front face of the panel is adapted to resist fragmentation or splintering when the front face of the panel is subjected to impact force.
 16. A panel as claimed in claim 15 wherein the back and/or front face of the panel is adapted to resist fragmentation or splintering by means of a flexible fragment containment layer located on the back and/or front face of the panel.
 17. A panel as claimed in claim 1 in which the facing or backing reinforcement comprises a plurality of layers of reinforcement sheets and/or rod arrays, and the material constituting one such layer is harder or lighter than the material constituting another such layer.
 18. A panel as claimed in claim 1 wherein panel support elements are incorporated in the matrix between facing and backing reinforcement to facilitate support of the panel in a structure including the panel.
 19. A panel as claimed in claim 1 wherein the facing and backing reinforcements each consist of a single interlaced rod array (ii). 